The invention relates to an air flow rate meter, and in particular to an air flow rate meter for an internal combustion engine which functions as a constant-temperature anemometer. The air flow rate meter of the category of the present invention comprise a resistive measurement bridge circuit, the bridge current flow being controllable in open-loop or closed-loop fashion in accordance with the voltage in the diagonal line of the bridge circuit.
A flow rate meter of this kind is known which has a temperature-dependent resistor in the air intake tube; this resistor is part of a resistor bridge circuit and is regulated in accordance with the bridge circuit diagonal voltage of the total flow of electric current to the bridge.
The output variable of this air flow rate meter is a voltage dependent on the air throughput kg/sec in the intake tube of the engine; at a throughput variation of from 1 to 40, this voltage varies only by approximately 1 to 3. Given this relatively undynamic behavior of the system, it is necessary for the air flow rate meter to be adjusted with the utmost precision to a set-point curve.
In the known air flow rate meter, this is attained by adjusting a bridge resistor at one point to the set-point value. Because of the tolerances of the electronic and mechanical components, however, the actual curve deviates from the set-point curve outside the adjustment point.
FIG. 1 shows the output signal U.sub.M of an air flow rate meter functioning as a constant-temperature anemometer in accordance with the prior art, plotted over the air throughput m. A set point characteristic curve 10, corresponding to set-point voltage U.sub.S, and an actual characteristic curve 11, corresponding to an actual voltage U.sub.A are shown. The two curves intersect at an adjustment point 12, and it is apparent that the maximum precision of the meter can be attained only at a single point on the curve.